Spectrum sensing is a technology used to identify unused or underutilized radio resources. For example, wide-band spectrum sensors are currently being developed.
One technology in which spectrum sensing is needed is cognitive radio.
The main emphasis on the development of spectrum sensing technology has been on algorithmic level.
Danijela Cabric, Artem Tkachenko, Robert W. Brodersen, “Experimental Study of Spectrum Sensing based on Energy Detection and Network Cooperation”, The 2nd Annual International Wireless Internet Conference (WICON), TAPAS Workshop, August, 2006, discusses feasibility of an energy detector in spectrum sensing.
Also collaborative or distributed spectrum sensing solutions have been proposed. Anu Huttunen, Juha Pihlaja, Visa Koivunen, Jari Junell and Kari Kalliojärvi, “Collaborative distributed spectrum sensing for cognitive radio”, Wireless World Research Forum Meeting 21, Stockholm, Sweden, 13-15 Oct. 2008, discusses one such solution.